Abstract
In this paper, large eddy simulation (LES) was adopted to simulate the cavitating flow in a waterjet pump with emphasis on the tip clearance flow. The numerical results agree well with the experimental observations, which indicates that the LES method can make good predictions of the unsteady cavitating flows around a rotor blade. The LES verification and validation (LES V&V) analysis was used to reveal the influence of cavitation on the flow structures. It can be found that the LES errors in cavitating region are larger than those in the non-cavitating area, which is mainly caused by more complicated cavitating and tip clearance flow structures. Further analysis of the interaction between the cavitating and vortex flow by the relative vorticity transport equation shows that the stretching, dilatation and baroclinic torque terms have major effects on the generation and transport of vortex structure. Meanwhile the Coriolis force term and viscosity term also exacerbate the vorticity transport in the cavitating region. In addition, the flow loss characteristics of this pump are also revealed by the entropy production theory. It is indicated that the tip clearance flow and trailing edge wake flow cause the viscous dissipation and turbulent dissipation, and the cavitation can further enhance the instability of the flow field in the tip clearance.
Highlights
Flow in velocity the Pumpfrom each transient result over all monitoring points around impeller blades is used for large eddy simulation (LES) verification and validation (V&V) analysis
The calculated hydrodynamic performance and the cavitation pattern are mainly compared with the experimental results, and the tip clearance flow and cavitation characteristics in the pump are analyzed mathematically by using the V&V method of LES
The numerical calculation method and the adopted grid and model can be proved to be suitable for simulating the transient cavitating flow in the pump; The LES error reflects the flow field around the rotor affected by transient cavitation and tip clearance flow to some extent
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Among the various turbulence models, the Shear-Stress-Transport (SST) model has good performance in capturing vertical structures such as TLV [10] In addition to this model, there are other models including k-ε, renormalization group k-ε (RNG) and the reynolds stress model (RNG) model; they have been adopted for the prediction of hydrodynamic performance and cavitation in rotating machinery, but they still could not yield more accurate numerical results in some complex cases [12]. This paper further makes use of LES V&V method for the analysis of the complex cavitating flow inside the waterjet pump The purpose of this investigation is to discuss the effect of cavitation on the flow field in a waterjet pump by the LES V&V method, with emphasis on the tip clearance flow. The impact of cavitation on the vorticity distributions and the flow loss features are discussed
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